Extending physical downlink control channels

ABSTRACT

Methods and apparatuses for transmitting and receiving at least one Downlink Control Information (DCI) in a communication system supporting Carrier Aggregation (CA) are provided. The method for receiving includes receiving information representative of presence of carrier indicator by higher layer signaling from a Node B; receiving information representative of at least one cell indicator by higher layer signaling from the Node B; defining an UE specific search space based on aggregation level, an UE ID, and at least one carrier indicator value, where the UE specific search space includes a set of Physical Downlink Control CHannel (PDCCH) candidates based on the aggregation level; decoding at least one PDCCH including at least one DCI respectively by the UE ID; and acquiring the at least one DCI, wherein the at least one carrier indicator value is based on the at least one cell indicator.

PRIORITY

This application is a Continuation Application of U.S. patentapplication Ser. No. 15/711,669, which was filed in the United StatesPatent and Trademark Office on Sep. 21, 2017, which is a ContinuationApplication of U.S. patent application Ser. No. 14/044,480, which wasfiled in the United States Patent and Trademark Office on Oct. 2, 2013,now U.S. Pat. No. 9,883,495, issued on Jan. 30, 2018, which is aContinuation Application of U.S. patent application Ser. No. 12/892,343,which was filed in the United States Patent and Trademark Office on Sep.28, 2010, now U.S. Pat. No. 9,295,043, issued on Mar. 22, 2016, andclaims priority under 35 U.S.C. § 119(e) to U.S. Provisional PatentApplication Nos. 61/246,380 and 61/246,387, which were both filed in theU.S. Patent and Trademark Office on Sep. 28, 2009, the entire contentsof each of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention is directed to wireless communication systems and,more specifically, to extending a Physical Downlink Control CHannel(PDCCH) from supporting communication in a single cell to supportingcommunication in multiple cells.

2. Description of the Art

A communication system includes a DownLink (DL) that supports thetransmissions of signals from a Base Station (BS) (or Node B) to UserEquipments (UEs), and an UpLink (UL) that supports transmissions ofsignals from UEs to the Node B. A UE, also commonly referred to as aterminal or a mobile station, may be fixed or mobile and may be awireless device, a cellular phone, a personal computer device, etc. ANode B is generally a fixed station and may also be referred to as aBase Transceiver System (BTS), an access point, or some other similarterminology.

The DL signals include data signals that carry information content,control signals, and Reference Signals (RS), which are also known aspilot signals. The Node B transmits data information to a UE through aPhysical Downlink Shared CHannel (PDSCH) and transmits controlinformation to a UE through a PDCCH.

The UL signals also include data signals, control signals, and RSs. A UEtransmits data information to the Node B through a Physical UplinkShared CHannel (PUSCH) and transmits control information through aPhysical Uplink Control CHannel (PUCCH). It is also possible for UEs totransmit control information through the PUSCH.

Downlink Control Information (DCI) serves several purposes and istransmitted in DCI formats through the PDCCH. For example, DCI formatsare used to provide DL Scheduling Assignments (SAs) for PDSCH receptionsby the UEs, UL SAs for PUSCH transmissions by the UEs, or TransmissionPower Control (TPC) commands for PUSCH receptions or PUCCH transmissionsfrom the UEs. DCI formats also provide scheduling information for aPaging CHannel (PCH), for a response by the Node B to Random AccessCHannels (RACH) transmitted by the UEs, and for Secondary InformationBlocks (SIBs) providing broadcast control information from the Node B.The DCI format for transmitting the TPC commands will be referred to asDCI format 3 and the DCI format for transmitting the schedulinginformation for the transmission of either PCH, RACH response, or SIBswill be referred to as DCI format 1C.

Typically, the PDCCH is a major part of the total DL overhead anddirectly impacts the achievable DL cell throughput. A conventionalmethod for reducing PDCCH overhead is to scale its size according to theresources required to transmit the DCI formats during a DL TransmissionTime Interval (TTI). Assuming Orthogonal Frequency Division MultipleAccess (OFDMA) as the DL transmission method, a Control Channel FormatIndicator (CCFI) parameter transmitted through the Physical ControlFormat Indicator CHannel (PCFICH) can be used to indicate the number ofOFDM symbols occupied by the PDCCH.

FIG. 1 is a diagram illustrating a structure for the PDCCH transmissionin the DL TTI, which for simplicity includes one sub-frame having M OFDMsymbols.

Referring to FIG. 1, the PDCCH 120 occupies the first N symbols 110. Theremaining M-N symbols of the sub-frame are assumed to be primarily usedfor PDSCH transmission 130. The PCFICH 140 is transmitted in somesub-carriers, also referred to as Resource Elements (REs), of the firstsymbol. The PCFICH includes 2 bits indicating a PDCCH size of M=1, M=2,or M=3 OFDM symbols. Additionally, some sub-frame symbols include RSREs, 150 and 160, which are common to all UEs for each of the Node Btransmitter antennas, which in FIG. 1 are assumed to be two. The RSsenable a UE to obtain a channel estimate for its DL channel medium andto perform various other measurements and functions. The PDSCH typicallyoccupies the remaining REs.

Additional control channels may be transmitted in the PDCCH region but,for brevity, they are not illustrated in FIG. 1. For example, to supportHybrid Automatic Repeat reQuest (HARQ) for PUSCH transmissions, aPhysical Hybrid-HARQ Indicator CHannel (PHICH) may be transmitted by theNode B, in a similar manner as the PCFICH, to indicate to groups of UEswhether or not their previous PUSCH transmission was received by theNode B.

The Node B separately codes and transmits each DCI format through aPDCCH.

FIG. 2 is a block diagram illustrating a conventional processing chainfor transmitting a DCI format.

Referring to FIG. 2, the Medium Access Control (MAC) layer IDentity ofthe UE (or UE ID), for which a DCI format is intended, masks the CyclicRedundancy Check (CRC) of the DCI format codeword in order to enable thereference UE to identify that the particular DCI format is intended forthe reference UE. The CRC 220 of the (non-coded) DCI format bits 210 iscomputed and is subsequently masked 230 using the eXclusive OR (XOR)operation between CRC bits and the UE ID 240, i.e., XOR(0,0)=0,XOR(0,1)=1, XOR(1,0)=1, and XOR(1,1)=0.

The masked CRC is then appended to the DCI format bits 250, channelcoding 260 is performed, for example, using a convolutional code,followed by rate matching 270 to the allocated PDCCH resources, and theninterleaving and modulation 280. Thereafter, a control signal 290 istransmitted.

A UE receiver performs the reverse operations of the Node B transmitterto determine whether a DCI format in the PDCCH was intended for the UE.

FIG. 3 is a block diagram illustrating a conventional processing chainfor receiving a DCI format.

Referring to FIG. 3, a received control signal, i.e., a PDCCH, 310 isdemodulated and the resulting bits are de-interleaved 320. Rate matchingapplied in the Node B transmitter is restored 330, and the output issubsequently decoded 340. After decoding, the DCI format bits 360 areobtained, after extracting the CRC bits 350, which are then de-masked370 by applying the XOR operation with the UE ID 380. Thereafter, the UEperforms a CRC test 390. If the CRC test passes, the UE considers theDCI format as being valid and determines the parameters for PDSCHreception (DL DCI format) or PUSCH transmission (UL DCI format). If theCRC test does not pass, the UE disregards the DCI format.

The information bits of the DCI format correspond to several InformationElements (IEs) such as, for example, the Resource Allocation (RA) IEindicating the part of the operating BandWidth (BW) allocated to a UEfor PDSCH reception or PUSCH transmission, the Modulation and CodingScheme (MCS) IE, the IE related to the HARQ operation, etc. The BW unitfor PDSCH or PUSCH transmissions is assumed to consist of several REs,e.g., 12 REs, and will be referred to as a Physical Resource Block(PRB).

PDCCHs for a UE are not transmitted at fixed and predetermined locationsand do not have predetermined coding rates. Consequently, a UE performsmultiple PDCCH decoding operations in each sub-frame to determinewhether any of the PDCCHs transmitted by the Node B are intended for theUE. In order to assist UEs with the multiple PDCCH decoding operations,the PDCCH REs are grouped into Control Channel Elements (CCEs) in thelogical domain. For a given number of DCI format bits as illustrated inFIG. 2, the number of CCEs for the respective PDCCH transmission dependson the channel coding rate. For UEs experiencing low or highSignal-to-Interference and Noise Ratio (SINR) in the DL, the Node B mayrespectively use a low or high channel coding rate in order to achieve adesired PDCCH BLock Error Rate (BLER). Therefore, a PDCCH transmissionto a UE experiencing low DL SINR typically requires more CCEs that aPDCCH transmission to a UE experiencing high DL SINR. Alternatively,different power boosting of CCE REs may also be used in order to achievea target BLER. Typical CCE aggregation levels for PDCCH transmissionsare assumed to follow a “tree-based” structure, for example, 1, 2, 4,and 8 CCEs.

For the PDCCH decoding process, a UE may determine a search space for acandidate PDCCH, after it restores the CCEs in the logical domain,according to a common set of CCEs for all UEs in a UE-Common SearchSpace (UE-CSS) and according to a UE-specific set of CCEs in aUE-Dedicated Search Space (UE-DSS). The UE-CSS includes the first C CCEsin the logical domain. The UE-DSS may be determined according to apseudo-random function having UE-common parameters as inputs, such asthe sub-frame number or the total number of PDCCH CCEs in the sub-frame,and UE-specific parameters such as the identity assigned to a UE (UEID).

For example, for CCE aggregation levels L ∈ {1,2,4,8}, the CCEscorresponding to PDCCH candidate m can be given by Equation (1).

L·{(Y _(k) +m)mod └N _(CCE,k) /L┘}+i  (1)

In Equation (1), N_(CCE,k) is a total number of CCEs in sub-frame k,i=0, . . . , L−1, m=0, . . . , M^((L))−1, and M^((L)) is a number ofPDCCH candidates for the respective CCE aggregation levels. Exemplaryvalues of M^((L)) for L ∈ {1,2,4,8} are, respectively, {6, 6, 2, 2}. Forthe UE-CSS, Y_(k)=0. For the UE-DSS, Y_(k)=(A·Y_(k-1))mod D where, forexample, Y⁻¹=UE_ID≠0, A=39827 and D=65537.

DCI formats conveying information to multiple UEs, such as DCI format 3or DCI format 1C, are transmitted in the UE-CSS. If enough CCEs remainafter transmitting DCI formats 3 and 1C, the UE-CSS may also convey someDCI formats for PDSCH receptions or PUSCH transmissions by UEs. TheUE-DSS exclusively conveys DCI formats for PDSCH receptions or PUSCHtransmissions. In an exemplary setup, the UE-CSS includes 16 CCEs andsupports 2 PDCCH with L=8 CCEs, or 4 PDCCH with L=4 CCEs, or 1 PDCCHwith L=8 CCEs and 2 PDCCH with L=4 CCEs. The CCEs for the UE-CSS areplaced first in the logical domain (prior to interleaving).

FIG. 4 illustrates a conventional PDCCH transmission process. Afterchannel coding and rate matching, as illustrated in FIG. 2, the encodedDCI format bits are mapped to CCEs in the logical domain.

Referring to FIG. 4, the first 4 CCEs (L=4), CCE1 401, CCE2 402, CCE3403, and CCE4 404 are used for DCI format transmission to UE1. The next2 CCEs (L=2), CCE5 411 and CCE6 412, are used for DCI formattransmission to UE2. The next 2 CCEs (L=2), CCE7 421 and CCE8 422, areused for DCI format transmission to UE3. The last CCE (L=1), CCE9 431,is used for DCI format transmission to UE4.

The DCI format bits may be scrambled 440 using a binary scrambling code,which is typically cell-specific, and are subsequently modulated 450.Each CCE is further divided into mini-CCEs. For example, a CCE including36 REs can be divided into 9 mini-CCEs, each having 4 REs.

Interleaving 460 is applied among mini-CCEs (blocks of 4 QPSK symbols).For example, a block interleaver may be used where the interleaving isperformed on symbol-quadruplets (4 Quadrature Phase Shift Keying (QPSK)symbols corresponding to the 4 REs of a mini-CCE) instead of onindividual bits. After interleaving the mini-CCEs, the resulting seriesof QPSK symbols may be shifted by J symbols 470, and then each QPSKsymbol is mapped to an RE 480 in the PDCCH region of the DL sub-frame.Therefore, in addition to the RS from the Node B transmitter antennas,491 and 492, and other control channels such as the PCFICH 493 and thePHICH (not shown), the REs in the PDCCH include QPSK symbolscorresponding to DCI format for UE1 494, UE2 495, UE3 496, and UE4 497.

In order to support higher data rates and signal transmission in BWslarger than the BWs of individual carriers (or cells) supporting legacycommunications, aggregation of multiple carriers (or cells) can be used.For example, to support communication over 100 MHz, aggregation of five20 MHz carriers (or cells) can be used. For ease of description, UEsthat can only operate over a single carrier (or cell) will be referredto herein as Legacy-UEs (L-UEs) while UEs that can operate over multiplecarriers (or cells) will be referred to herein as Advanced-UEs (A-UEs).

FIG. 5 illustrates a principle of carrier aggregation. An operating BWof 100 MHz includes the aggregation of 5 (contiguous, for simplicity)carriers, 521, 522, 523, 524, and 525, each having a BW of 20 MHz.Similarly to the sub-frame structure for communication over a singlecarrier in FIG. 1, the sub-frame structure for communication overmultiple carriers includes a PDCCH region, for example, 531 through 535,and a PDSCH region, for example, 541 and 545.

FIG. 6 is a diagram illustrating a conventional heterogeneous networkdeployment.

Referring to FIG. 6, an area covered by a macro-Node B 610 encompassesareas covered by micro-Node Bs 620 and 630. Because the macro-Node Bcovers a larger area than a micro-Node B, its transmission power issubstantially larger than the transmission power of a micro-Node B.Consequently, for topologies such as illustrated in FIG. 6, the signalstransmitted by a macro-Node B can cause severe interference to thesignals transmitted by a micro-Node B. Interference coordinationtechniques can be applied to PDSCH transmissions to mitigatemacro-to-micro interference using different PRBs between PDSCH signaltransmissions from the macro-Node B and a micro-Node B. However, suchinterference coordination is not possible for the PDCCH because the CCEsare pseudo-randomly distributed over the entire operating BW, as waspreviously described.

To avoid interference to PDCCH transmissions in a micro-cell, all PDCCHtransmissions can be in the macro-cell and a Carrier Indicator, or CellIndicator, (CI) IE can be introduced in the DCI formats to indicatewhether the DCI format is for the macro-cell or for the micro-cell. Forexample, a CI IE of 2 bits can indicate whether the DCI format is forthe macro-cell or for any of a maximum of three micro-cells.

In addition to providing PDCCH interference avoidance, PDCCHtransmission in certain cells may be avoided for practical reasons. Forexample, it is desirable to avoid PDCCH transmissions in cells withsmall BW as they are inefficient and lead to large respective overhead.Also, PDSCH transmissions in a cell can be optimized to occur over allDL sub-frame symbols if transmissions of PDCCH and of other supportingsignals such as UE-common RS, are avoided.

The CI functionality can accommodate:

PUSCH scheduling in the UL of multiple cells through PDCCH transmissionin a single cell;

PDSCH scheduling in the DL of multiple cells through PDCCH transmissionin a single cell; and

PDCCH transmission in a first cell (macro-cell) and in a second cell(micro-cell).

FIG. 7 is a diagram illustrating a conventional PUSCH scheduling in theUL of multiple cells through PDCCH transmission in a single cell.

Referring to FIG. 7, a PDCCH in a single cell 710 is associated with theUL of two cells, 720 and 730. Consequently, PDCCHs scheduling PUSCHtransmissions from Cell 1 and Cell 2 are transmitted in a single celland the cell of PUSCH transmission can be identified by a CI IEconsisting of 1 bit.

FIG. 8 is a diagram illustrating a conventional PDSCH scheduling in a DLof multiple cells through PDCCH transmission in a single cell.

Referring to FIG. 8, only Cell1 810 and Cell3 830 transmit PDCCH.Scheduling for Cell2 820 is performed through PDCCH transmission inCell1 810 and scheduling for Cell4 840 and Cell5 850 is performedthrough PDCCH transmissions in Cell3 830.

FIG. 9 is a diagram illustrating a conventional PDCCH transmission in afirst cell (macro-cell) and in a second cell (micro-cell), which mayoccur to avoid interference in PDCCH transmissions between a macro-celland a micro-cell.

Referring to FIG. 9, although both macro-cell and micro-cell may havePDSCH transmissions in Cell1 910 and Cell2 920, the macro-cell transmitsPDCCH only in Cell1 910 and the micro-cell transmit PDCCH only in Cell2920.

One issue for supporting PDCCH transmissions using a CI is the PDCCHsize. In communication systems having a single cell, the PDCCH isassumed to be limited to a maximum number of M OFDM symbols. Incommunication systems having multiple cells and having PDCCHtransmission in a single cell, this limitation of the PDCCH size maycause scheduling restrictions. In general, the PDCCH size may need to beincreased if the PDCCH in one cell performs scheduling in multiplecells.

For the UE-CSS, which is assumed to include a fixed number of CCEs, itmay not be possible to transmit additional PDCCH corresponding toadditional cells.

For the UE-DSS, modification and expansion is needed in order totransmit multiple DCI formats to a UE in the PDCCH region of a singlecell.

For the blind decoding operations a UE needs to perform, their numbermay scale linearly with the number of cells for which PDCCH istransmitted in a single cell. It is desirable to avoid such an increasein order to avoid the associated impact on the UE receiver complexity.

Therefore, there is a need to expand the PDCCH region in a single cellto support PDCCH transmissions for scheduling in multiple cells.

There is a further need to expand the UE-CSS in a single cell to enablePDCCH transmission conveying UE-common information for multiple cells.

There is another need to expand the capacity of the UE-DSS in a singlecell for scheduling over multiple cells.

Additionally, there is another need to reduce the number of blinddecoding operations a UE needs to perform.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been designed to solve at leastthe aforementioned limitations and problems in the prior art and toprovide the following advantages. An aspect of the present invention isto provide methods and apparatus for expanding a control region in asingle cell from supporting transmission of DCI to a UE forcommunication over the single cell to supporting transmission of DCI tothe UE for communication over multiple cells.

According to an aspect of the present disclosure, a method formonitoring downlink control information in a communication system forsupporting a plurality of cells is provided that includes acquiring acell index for a cell, the cell index being defined based on a dedicatedradio resource control (RRC) signaling; acquiring information for anorthogonal frequency division multiplex (OFDM) symbol and a resourceblock through the dedicated RRC signaling; and monitoring a physicaldownlink control channel (PDCCH) on a dedicated search space associatedwith the information, the dedicated search space being defined per eachof the plurality of cells; and receiving a physical downlink sharedchannel (PDSCH) on the cell based on the monitored PDCCH, the cell beingone among the plurality of cells, wherein the dedicated search space isdefined based on an aggregation level, a number of PDCCH candidate forthe aggregation level, and an identifier configured for a user equipment(UE).

According to another aspect of the present disclosure, a method isprovided for transmitting downlink control information in acommunication system for supporting a plurality of cells, the methodincluding transmitting information on a cell index for a cell, the cellindex being defined based on a dedicated radio resource control (RRC)signaling; transmitting information for an orthogonal frequency divisionmultiplex (OFDM) symbol and a resource block through the dedicated RRCsignaling; and transmitting a physical downlink control channel (PDCCH)on a dedicated search space associated with the information, thededicated search space being defined per each of the plurality of cells;and transmitting a physical downlink shared channel (PDSCH) on the cellbased on the transmitted PDCCH, the cell being one among the pluralityof cells, wherein the dedicated search space is defined based on anaggregation level, a number of PDCCH candidate for the aggregationlevel, and an identifier configured for a user equipment (UE).

According to a further aspect of the present disclosure, an apparatus isprovided for monitoring downlink control information in a communicationsystem for supporting a plurality of cells, the apparatus including atransceiver configured to transmit and receive a signal; and a processorcoupled with the transceiver, with the processor being configured toacquire a cell index for a cell, the cell index being defined based on adedicated radio resource control (RRC) signaling; acquire informationfor an orthogonal frequency division multiplex (OFDM) symbol and aresource block through the dedicated RRC signaling; and monitor aphysical downlink control channel (PDCCH) on a dedicated search spaceassociated with the information, the dedicated search space beingdefined per each of the plurality of cells; and control the transceiverto receive a physical downlink shared channel (PDSCH) on the cell basedon the monitored PDCCH, the cell being one among the plurality of cells,wherein the dedicated search space is defined based on an aggregationlevel, a number of PDCCH candidate for the aggregation level, and anidentifier configured for a user equipment (UE).

According to another aspect of the present disclosure, an apparatus fortransmitting downlink control information in a communication system forsupporting a plurality of cells is provided, with the apparatusincluding a transceiver configured to transmit information on a cellindex for a cell, the cell index being defined based on a dedicatedradio resource control (RRC) signaling; transmit information for anorthogonal frequency division multiplex (OFDM) symbol and a resourceblock through the dedicated RRC signaling; and transmit a physicaldownlink control channel (PDCCH) on a dedicated search space associatedwith the information, the dedicated search space being defined per eachof the plurality of cells; and transmit a physical downlink sharedchannel (PDSCH) on the cell based on the transmitted PDCCH, the cellbeing one among the plurality of cells, wherein the dedicated searchspace is defined based on an aggregation level, a number of PDCCHcandidate for the aggregation level, and an identifier configured for auser equipment (UE).

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentinvention will be more apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram illustrating a conventional structure for PDCCHtransmission;

FIG. 2 is a block diagram illustrating a conventional processing chainfor transmitting a DCI format;

FIG. 3 is a block diagram illustrating a conventional processing chainfor receiving a DCI format;

FIG. 4 is a diagram illustrating a conventional PDCCH transmissionprocess;

FIG. 5 is a diagram illustrating a principle of carrier aggregation;

FIG. 6 is a diagram illustrating a conventional heterogeneous networkdeployment;

FIG. 7 is a diagram illustrating a conventional PUSCH scheduling in a ULof multiple cells through PDCCH transmission in a single cell;

FIG. 8 is a diagram illustrating a conventional PDSCH scheduling in a DLof multiple cells through PDCCH transmission in a single cell;

FIG. 9 is a diagram illustrating a conventional PDCCH transmission in afirst cell (macro-cell) and in a second cell (micro-cell);

FIG. 10 is a diagram illustrating a method of informing an A-UE whethera CI IE is included in DCI formats in a UE-specific manner, according toan embodiment of the present invention;

FIG. 11 is a diagram illustrating an E-PDCCH multiplexing structurewhere A-UEs assume a maximum PDCCH size to determine a first E-PDCCHsymbol, according to an embodiment of the present invention;

FIG. 12 is a diagram illustrating an E-PDCCH multiplexing structurewhere A-UEs decode a PCFICH to determine an actual PDCCH size and afirst E-PDCCH symbol, according to an embodiment of the presentinvention;

FIG. 13 is a diagram illustrating an assignment of different CI valuesto different cells, according to an embodiment of the present invention;

FIG. 14 is a diagram illustrating placement of CCEs for multiple UE-CSS,according to an embodiment of the present invention;

FIG. 15 is a diagram illustrating an operation for generating a distinctUE-DSS for each cell through a respective distinct initialization of avariable determining the location of a UE-DSS, according to anembodiment of the present invention;

FIG. 16 is a diagram illustrating an extension of a PDCCH size byconfiguring a set of possible values and using a PCFICH to indicate onevalue in the set, according to an embodiment of the present invention;and

FIG. 17 is a diagram illustrating a combination of explicit and implicitindication by a Node B of a UE-CSS size, according to an embodiment ofthe present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Various embodiments of the present invention will now be described indetail with reference to the accompanying drawings. This invention may,however, be embodied in many different forms and should not be construedas limited to the embodiments set forth herein. Rather, theseembodiments are provided so that this disclosure will be thorough andcomplete and will fully convey the scope of the invention to thoseskilled in the art.

Additionally, although the present invention is described in relation toan Orthogonal Frequency Division Multiple Access (OFDMA) communicationsystem, it also applies to Frequency Division Multiplexing (FDM) systemsand to Single-Carrier Frequency Division Multiple Access (SC-FDMA),OFDM, FDMA, Discrete Fourier Transform (DFT)-spread OFDM, DFT-spreadOFDMA, SC-OFDMA, and SC-OFDM.

In accordance with an embodiment of the present invention, an A-UE issemi-statically configured, for example, through Radio Resource Control(RRC) signaling, the cells over which it may have PDSCH reception orPUSCH transmission. A link between the DL and the UL in those cells mayalso be configured. The inclusion of the CI IE in DCI formats can beeither UE-specific or cell-specific. When the CI IE in DCI formats isUE-specific, each A-UE is informed through higher layer signaling (MACor RRC signaling) whether its assigned DCI formats in a cell include aCI IE. When the CI IE in DCI formats is cell-specific, the Node B maybroadcast whether a CI IE is included in the DCI formats. In both cases,the values of the CI to be monitored by an A-UE are also included. TheDCI formats having the CI IE may be all DCI formats or a predeterminedsubset of DCI formats. For example, DCI formats in the UE-CSS may notcontain CI while DCI formats in the UE-DSS may contain CI.

FIG. 10 is a diagram illustrating a method of informing an A-UE whethera CI IE is included in DCI formats in a UE-specific manner, according toan embodiment of the present invention.

Referring to FIG. 10, an A-UE is configured in the DL of Cell1 1010,Cell2 1020, and Cell3 1030 for PDSCH reception and in the UL of Cell11040 and Cell2 1050 for PUSCH transmission. The cells of PDCCHtransmission are also informed to the A-UE through higher layersignaling.

In FIG. 10, a PDCCH is transmitted only in Cell1 1060. For example, theDL and UL for Cell1 may correspond to a macro-cell, while the DL and ULof Cell2 may correspond to a first micro-cell and the DL of Cell3, andthe UL of Cell2 can correspond to a second micro-cell. DCI formatsassociated with PUSCH transmissions or with TPC for PUSCH or PUCCHtransmissions (DCI format 3) will be referred to as UL DCI formats. Theremaining DCI formats are associated with PDSCH receptions and will bereferred to as DL DCI formats.

For the setup in FIG. 10, DL DCI formats to the UE include a CI IEhaving 2 bits. For example, for the DL, the CI values of ‘00’, ‘01”, and“10” can correspond to Cell1, Cell2, and Cell3, respectively, while theCI value “11” is unused. Similarly, for the UL, the CI values of ‘0’ and“1” can correspond to Cell1 and Cell2, respectively. In general, thenumber of bits for the CI IE can be different between DL DCI formats andUL DCI formats (including, for example, not having any CI IE bits in ULDCI formats while having CI IE bits in DL DCI formats). The associationbetween CI values and Cells may also be implicitly determined. Forexample, ascending CI values of “00”, “01”, “10”, and “11” can be mappedto Cells in order of increasing carrier frequency.

The use of CI to indicate the cell for which a DCI format is intendedmay not be necessary for cells with different BWs because the respectiveDCI formats may have different sizes. For example, for 2 cells, wherethe PDCCH is transmitted only in one cell, the CI inclusion in the DLDCI formats is not necessary if, for example, one cell has a BW of 20MHz and the other cell has a BW of 5 MHz. In general, the primary reasonfor having a different DCI format size for different BWs is the ResourceAllocation (RA) IE in the DCI formats, which should have a larger sizefor cells with larger BWs, as it addresses a larger number of PRBs.

The transmission of DCI formats to L-UEs is supported with theconventional PDCCH structure. The PDCCH transmission to A-UEs havingPDSCH reception or PUSCH transmission in the same cell is also supportedwith the conventional PDCCH structure. There is no differentiationbetween these A-UEs and the L-UEs with respect to the PDCCHtransmission, although different DCI formats may be used. For ease ofreference, such A-UEs will be referred to as Primary-UEs (P-UEs) and thecell with the PDCCH transmission as Primary-cell (Pcell). Conversely,A-UEs having PDSCH reception or PUSCH transmission in a cell other thanthe Pcell will be referred to as Secondary-UEs (S-UEs) and thecorresponding cells as Secondary-cells (Scells).

For example, in FIG. 10, UEs receiving PDSCH in Cell1 are P-UEs andCell1 is the Pcell, while UEs receiving PDSCH in Cell2 are S-UEs andCell2 is an Scell. An A-UE can be both a P-UE and an S-UE depending onthe cell (Pcell or Scell, respectively). Therefore, the classificationof an A-UE as a P-UE or an S-UE is unique for each cell and may bedifferent among cells as an A-UE can be a P-UE in the Pcell and the S-UEin an Scell.

For the PDCCH transmission to S-UEs in Scells, the conventional PDCCHstructure or a separate PDCCH structure may be used. For example, forlightly loaded systems for which the capacity (first M OFDM symbols ofthe DL sub-frame) of the conventional PDCCH structure is not reached forscheduling P-UEs, it is also possible to support the transmission of DCIformats to S-UEs while, for heavily loaded systems, an additional PDCCHstructure may be needed to support the PDCCH transmission to S-UEs.

Whether the conventional PDCCH structure or an Extended PDCCH (E-PDCCH)structure is used can be predetermined or be informed by the Node Bthrough broadcast signaling or through UE-specific higher layersignaling. The PDCCH CCEs for an A-UE can be either in the PDCCH or inthe E-PDCCH, but not in both. Whether an A-UE monitors the PDCCH or theE-PDCCH for scheduling a PDSCH or a PUSCH in a specific cell can besemi-statically configured either through higher layer signaling orthrough broadcast signaling.

If the E-PDCCH in the Pcell is used for scheduling a PDSCH or a PUSCH inScells, the following is considered, in accordance with an embodiment ofthe present invention:

E-PDCCH Contents

The E-PDCCH provides an extension to the PDCCH and therefore, conveysinformation of the same nature. In addition to DCI formats for S-UEs,the E-PDCCH may include a respective PCFICH (referred to as an E-PCFICH)and a PHICH (referred to as an E-PHICH) for PUSCH transmissions inScells served by the E-PDCCH. The E-PCFICH and the E-PHICH have the samestructure as the PCFICH and the PHICH, respectively.

Frequency Resources for E-PDCCH

The DCI formats in the E-PDCCH are transmitted in CCEs, but the CCEallocation is in PRBs as the E-PDCCH is orthogonally multiplexed withthe PDSCH. The PRBs for the E-PDCCH can be semi-statically ordynamically configured. A semi-static configuration of E-PDCCH PRBsensures adequate separation in the frequency domain in order to obtainfrequency diversity or that the PRBs are selected according to aninterference co-ordination technique minimizing interference fromadjacent cells.

Time Resources for E-PDCCH

The first E-PDCCH symbol can be the first OFDM symbol after the lastactual PDCCH OFDM symbol or the first symbol after the last PDCCH OFDMsymbol, assuming the maximum number of PDCCH OFDM symbols. When thefirst E-PDCCH symbol is the first OFDM symbol after the last actualPDCCH OFDM symbol, S-UEs decode the PCFICH to determine the E-PDCCHstart. When the first E-PDCCH symbol is the first symbol after the lastPDCCH OFDM symbol assuming the maximum number of PDCCH OFDM symbols,maximum E-PDCCH decoding latency results, but errors from incorrectPCFICH detection, which will lead in PDCCH decoding failure, areavoided.

The last E-PDCCH symbol can be statically, semi-statically, ordynamically configured. With static configuration, the last E-PDCCHsymbol can be, for example, the seventh symbol of the DL sub-frame. Withsemi-static configuration, the last E-PDCCH symbol can be informed bythe Node B through a broadcast channel With dynamic configuration, thelast E-PDCCH symbol can be informed through the E-PCFICH.

The range of OFDM symbols indicated by the E-PCFICH for the E-PDCCH canbe different than the range of OFDM symbols indicated by the PCFICH forthe PDCCH. For example, the E-PCFICH may also indicate 0 OFDM symbolsfor the E-PDCCH in which case the E-PCFICH and the E-PHICH may betransmitted in the PDCCH.

FIG. 11 illustrates an E-PDCCH multiplexing structure where A-UEs assumea maximum PDCCH size to determine a first E-PDCCH symbol, according toan embodiment of the present invention.

Referring to FIG. 11, the PDCCH transmission 1110 has 2 OFDM symbols,out of a maximum of 3 PDCCH OFDM symbols. The first E-PDCCH symbol isthe first OFDM symbol after the PDCCH transmission, assuming the maximumof 3 OFDM symbols. Therefore, the first E-PDCCH symbol is the fourthOFDM symbol of the DL sub-frame. The E-PCFICH transmission (not shown)is always in the first E-PDCCH symbol and, for the structure of FIG. 11,it indicates that the E-PDCCH is transmitted in 2 OFDM symbols 1120. TheE-PDCCH transmission PRBs 1130 are semi-statically configured throughbroadcast signaling by the Node B (for example, in an SIB). The E-PDCCHtransmission is multiplexed with PDSCH transmissions to various UEs,1140, 1150, and 1160. PDSCH transmissions to L-UEs may or may not occurin PRBs used for E-PDCCH transmission. As an L-UE cannot be aware of theE-PDCCH existence, if it is assigned PDSCH reception in E-PDCCH PRBs, itwill treat such PRBs as PRBs that include a PDSCH. Although this willdegrade the PDSCH reception quality for the L-UEs, it is up to the NodeB to determine whether or not perform such scheduling. A-UEs can beaware of the E-PDCCH PRBs and apply the appropriate rate matching fortheir respective PDSCH receptions.

FIG. 12 illustrates an E-PDCCH multiplexing structure where A-UEs decodea PCFICH to determine an actual PDCCH size and a first E-PDCCH symbol,according to an embodiment of the present invention.

Referring to FIG. 12, a PDCCH transmission 1210 has 2 OFDM symbols. Thefirst E-PDCCH symbol is the third OFDM symbol, which is the first OFDMsymbol after the PDCCH transmission. The E-PCFICH transmission (notshown) is always in the first E-PDCCH symbol and, in the structureillustrated in FIG. 12, it indicates that the E-PDCCH is transmitted in2 OFDM symbols 1220. The E-PDCCH transmission PRBs 1230 arepredetermined.

If the transmission of DCI formats for multiple Scells is conveyedthrough the E-PDCCH, in accordance with an embodiment of the presentinvention, all E-PDCCH CCEs are jointly considered for all Scells,instead of having a separate set of CCEs for each S cell. Therefore,there is only a single set of CCEs in the E-PDCCH, where each S-UE mayhave its UE-CSS and its UE-DSS. This also enables the transmission of asingle E-PCFICH, instead of multiple E-PCFICH with each onecorresponding to a different Scell in the E-PDCCH.

UE-CSS

In a first alternative, the UE-CSS for S-UEs is separately configuredand its size, in number of CCEs, may be broadcasted by the Node B. Forexample, the UE-CSS size may take one of four predetermined values andthe Node B broadcasts 2 bits to indicate that value (for example,through an SIB in the Pcell) or to indicate that the UE-CSS size iseither 1, 2, 3, or 4 times a basic size of K CCEs. The CCEs for theUE-CSS in the E-PDCCH are placed first, i.e., before the CCEs for theUE-DSS. Once an S-UE is informed of the UE-CSS size, it needs todetermine the CCEs corresponding to each Scell.

In a first option for the first alternative, the S-UE is informed of theorder of Scells either through higher layer signaling, for UE-specificCI configuration, or as part of the system information for cell-specificCI configuration. This is equivalent to an S-UE being informed of the CIvalue for its DCI formats. In case a CI may not exist, such as, forexample, when the cells have unequal BWs, the order may be in terms ofdecreasing BWs, e.g., the larger BWs are ordered first.

FIG. 13 is a diagram illustrating an assignment of different CI valuesto different cells, according to an embodiment of the present invention.

Referring to FIG. 13, the CCEs for the UE-CSS of the macro-cell 1310 areplaced in the PDCCH. The CCEs for the UE-CSS for micro-cell 1 1320 areordered first in the E-PDCCH (CI=1) and the CCEs for the UE-CSS formicro-cell 2 1330 are ordered second in the E-PDCCH (CI=2). Once the CIvalues have been assigned to Scells, the CCEs of the UE-CSS of S-UEs areplaced in the same order in the logical domain.

FIG. 14 is a diagram illustrating placement of CCEs for multiple UE-CSS,according to an embodiment of the present invention.

Referring to FIG. 14, the L₁ CCEs for a first UE-CSS of S-UEs(micro-cell 1 or for a first set of S-UEs, CI=1) are placed first 1410,followed by the L₂ CCEs for a second UE-CSS of S-UEs (micro-cell 2 orfor a second set of S-UEs, CI=2) 1420. The placement of the CCEs for theUE-DSS 1430 occurs after the placement of the CCEs for the UE-CSS in thelogical domain. The number of CCEs of the UE-CSS for S-UEs for thedifferent CI values, denoted by L₁ and L₂ in FIG. 14, may be implicitlydetermined from the total UE-CSS size or may be informed by the Node Bthrough broadcast signaling. Alternatively, the number of CCEs for theUE-CSS of S-UEs can be the same for all CI values, regardless of the DLor UL operating BW in each Scell (that is, L₁=L₂ in FIG. 14).

The CCEs for the UE-CSS of S-UEs are ordered as illustrated in FIG. 14to reduce the associated number of Blind Decoding Operations (BDOs)because, for each UE-CSS, an S-UE searches a sub-set of the total set ofCCEs allocated to the total UE-CSS. Moreover, by ordering the UE-CSSsfor S-UEs, it is not necessary to include the CI IE in DCI formatstransmitted in each UE-CSS.

In a second option for the first alternative, the ordering of individualUE-CSS for S-UEs is not applied and the respective CCEs may bedistributed over the entire set of CCEs for the total UE-CSS.Thereafter, CI inclusion in the DCI formats is performed and the UEsearch process for DCI formats can be performed for the UE-DSS of S-UEsas will be described below.

In a second alternative, the UE-CSS remains unchanged, the S-UEs aretreated as P-UEs with respect to the transmission of DCI format 3 andDCI format 1C in Scells, and there is no differentiation of UEs intodifferent categories with respect to the UE-CSS.

The PCH can be transmitted to all S-UEs in the cell with the PDCCHtransmission (Pcell).

Assuming no transmission of synchronization signals from cells (such asmicro-cells) without PDCCH transmission (Scells), S-UEs acquire thesynchronization signal of the cell (such as a macro-cell) with PDCCHtransmission (Pcell). Thereafter, the RACH process is completed throughthe Pcell and no additional RACH response signaling, corresponding tocells without PDCCH transmission (S cells), is necessary.

The SIBs for cells (such as micro-cells) without PDCCH transmission(Scells) can also be transmitted from the cell (such as macro-cell) withPDCCH transmission (Pcell) using different CRC masks in DCI format 1C toindicate the cell corresponding to the SIB transmission.

DCI format 3 multiplexes TPC commands corresponding to UEs in the cell(such as a macro-cell) with PDCCH transmission (Pcell) and to UEs in thecells (such as micro-cells) without PDCCH transmission (Scells).

Accordingly, P-UEs have their UE-CSS for DCI format transmission in thePDCCH as in a backward compatible system including a single cell. ForS-UEs, either a new UE-CSS is defined in the E-PDCCH, as described abovein the first alternative, or no additional UE-CSS is defined and all UEs(P-UEs and S-UEs) use the same UE-CSS in the PDCCH, as described abovein the second alternative.

UE-DSS

For the UE-DSS and single-cell operation, using the previously definednotation, the CCEs corresponding to a PDCCH candidate m are given byEquation (2).

S _(k) ^((L)) =L·{(Y _(k) +m)mod └N _(CCE,k) /L┘}+i  (2)

In Equation (2), N_(CCE,k) is the total number of CCEs in sub-frame k,i=0, . . . , L−1, m=0, . . . , M^((L))−1, and M^((L)) is the number ofcandidates in the UE-DSS.

The above UE-DSS structure leads to identical UE-DSSs for differentcells (Pcell or Scells) as they are assumed to share the same UE-DSS inthe E-PDCCH (or in the PDCCH when it supports the transmission of DCIformats for multiple cells).

In order to provide distinct UE-DSS, in addition to the UE_ID, inaccordance with an embodiment of the present invention, the UE-DSS alsodepends on the Cell_ID. This can substantially decrease the probabilitythat a DCI format transmission is blocked due to the unavailability ofCCEs in the UE-DSS. Reducing this blocking probability increases theprobability that a PDSCH or PUSCH scheduling occurs and therefore,improves the respective DL or UL system throughput and enhancesoperating quality and reliability.

The Cell_ID may be the CI value allocated to each cell. For example, theUE may be informed of the Cell_ID through higher layer signaling. Atleast when the cells have equal BWs (and a respective CI is defined),the Cell_ID may be the same as the respective CI. The UE may obtain theCell_ID during initial synchronization with the respective cell, or ifthe cell does not transmit synchronization signals, the UE may obtainthe respective Cell_ID through higher layer signaling from the celltransmitting synchronization signals after synchronization.Additionally, the Cell_ID may be UE-specific and informed to each UEthrough higher layer signaling. For example, for 3 cells, instead ofhaving three different respective Cell_IDs, the Cell_ID for each UE candepend on the number of cells the UE is configured for. If UE1 isconfigured for Cell1 and Cell2, the respective Cell_IDs can be Cell_ID1and Cell_ID2. If UE2 is configured for Cell2 and Cell3, the respectiveCell_IDs can also be Cell_ID1 and Cell_ID2.

The following example further demonstrates the occurrence oftransmission blocking for a DCI format. Assuming that DCI formats to aUE are transmitted with 4 CCEs, then, as there are only 2 candidates inthe UE-DSS for this CCE aggregation level, transmission of DCI formatsfor at most 2 cells can be supported (or one cell, for both PDSCHreception and PUSCH transmission). Also, due to randomization throughinterleaving, the UE-DSSs for different UEs may have overlapping CCEs,and for this reason it will often be likely that the transmission of aDCI format for only a single cell can be supported.

An embodiment of the invention to construct separate UE-DSS for eachcell considers that the initialization of the variable Y_(k) includesthe Cell_ID. When 0⊕0=0, 0⊕1=1, 1⊕0=1, 1⊕1=0, where ⊕ denotes the binarymodulo add operation, an A-UE receives multiple PDSCH or transmitsmultiple PUSCH in multiple cells while the respective DCI formats aretransmitted in a single cell, and Y⁻¹=(UE_ID)⊕(Cell_ID)≠0 for the UE-DSSof the respective cell.

FIG. 15 illustrates an initialization of a variable Y_(k) with a Cell_IDaccording to an embodiment of the present invention.

Referring to FIG. 15, the binary UE_ID 1510 and the binary Cell_ID 1520are added by a binary adder 1530 to provide the initial value Y⁻¹ 1540of the variable Y_(k), randomizing the CCEs in the UE-DSS in sub-frame kfor DCI formats corresponding to the respective cell. Assuming a 16-bitUE ID, the requirement Y⁻¹≠0 prevents the use of a small number ofUE_IDs, which has only a minor impact on the total number of 2¹⁶=65536available UE Ids, considering that the total number of cells for whichthe DCI formats are transmitted in a single cell is less than 10. Also,as the variable Y_(k) depends on the Cell_ID, it should be denoted asY_(k) ^(c) with c=0, 1, . . . , N_(c)−1, where N_(c) is the number ofcells for which the respective DCI formats are conveyed in a single cell(Pcell).

In another embodiment of the invention to construct separate UE-DSS foreach cell, denoting as ƒ(c) a function of the CI or of the Cell_ID forcell c, each UE-DSS can be obtained by Equation (3).

S _(k,c) ^((L)) =L·{(Y _(k) +m+ƒ(c))mod └N _(CCE,k) /L┘}+i  (3)

One condition for S_(k,c) ^((L)) may be that the UE-DSS corresponding toPDSCH/PUSCH scheduling in the Pcell should be defined as for L-UEs. Thisis useful for maintaining the legacy operation when all cells, otherthan the Pcell, are deactivated. Therefore, if c_(P) is the CI orCell_ID for the Pcell, then ƒ(c_(P))=0.

For CI or Cell_ID values c other than c_(P), ƒ(c) may be determined asƒ(c)=1, 2, . . . , 7 (assuming a 3-bit CI), which can be ranked inascending order based on the assigned CI values. Only active cells areconsidered in order to reduce the self-blocking probability for theUE-DSS of an A-UE. The exact values for Scells (excluding the Pcell) arenot material as long as they are consecutive and the conditionƒ(c_(P))=0 is satisfied for the Pcell. For example, for CI or Cell_IDvalues c other than c_(P), the function ƒ(c) may be determined asƒ(c)=−3,−2,−1,1,2,3, or in general, by alternating assignments ofpositive and negative integer values in a consecutive manner aroundƒ(c_(P))=0 (starting from 1, and continuing with −1, 2, −2, and so on).

The transmission of DCI formats for scheduling in multiple S cellsincreases the number of BDOs an A-UE performs. Without any restrictionsin the locations of these possible DCI formats, this increase in thenumber of BDOs is linear with the number of Scells. This increases theUE receiver complexity and also increases the probability of a false CRCtest (resulting to a UE incorrectly considering a DCI format as intendedfor it).

Several alternative designs exist for reducing the number of BDOs. Allconsider that the possible locations of DCI formats in the multipleUE-DSSs for a reference UE are mutually dependent. In addition toreducing the number of BDOs and CRC tests, these designs maintain thesame receiver architecture (bank of decoders) for the basic single-cellUE-DSS decoding process regardless of the number of cells a UE isconfigured.

A first design uses the same aggregation level L for all DCI formats toa reference UE. If for the reference cell c₁ a candidate m is identifiedby the UE in position L·{(Y_(k) ^(c) ¹ +m)mod └N_(CCE,k)/L┘}+i, m=0, . .. , M^((L))−1, i=0, . . . , L−1, an additional cell c₂ can have apotential candidate n in position L·{(Y_(k) ^(c) ¹ +m)mod└N_(CCE,k)/L┘}+i, n=0, . . . , M^((L))−1. Therefore, after the UEidentifies a DCI format for cell c₁, it performs an additional M^((L))BDOs (for n=0, . . . M^((L))−1) to determine if it also has one for cellc₂.

A second design enables different aggregation levels to be used for thePDCCH, but imposes a restriction in the possible candidates for eachaggregation level. If for cell c₁ a PDCCH is identified for candidate min position L·{(Y_(k) ^(c) ¹ +m)mod └N_(CCE,k)/L┘}+i, m=0, . . . ,M^((L))−1, i=0, . . . L₁−1, an additional cell c₂ can have a potentialPDCCH candidate in position L₂·{(Y_(k) ^(c) ² +m·mod(min(L₁, L₂)))mod└N_(CCE,k)/L₂┘}+j, j=0, . . . , L₂−1. Therefore, after the UE identifiesa PDCCH for cell c₁, it performs a number additional BDOs equal to thenumber of possible aggregation levels to determine if it also has aPDCCH for cell c₂. In accordance with an embodiment of the presentinvention, this number of additional BDOs is 4, as the possibleaggregation levels are {1,2,4,8}. This process can directly extend toadditional cells.

A third design is a combination of the first and second designs, wherethe aggregation level used for the PDCCH in a reference cell (Pcell)affects the possible aggregation levels for the PDCCH for the remainingcells (Scells) for which a UE is configured. For example, theaggregation levels used for the PDCCH for the remaining cells may onlyhave the same or the next larger value relative to the one used for thePDCCH for the reference cell (if L=8 is used in the reference cell, thenL=8 is also used in the remaining cells). Additionally, the position ofthe PDCCH for the reference cell affects the possible PDCCH positionsfor the remaining cells. For example, if the PDCCH position for thereference cell is odd or even numbered, then the position of thepotential PDCCH for the remaining cells is also odd or even numbered,respectively. Therefore, for the third design, if for the cell c₁ aPDCCH is identified for candidate m in position L₁·{(Y_(k) ^(c) ¹ +m)mod└N_(CCE,k)/L₁┘}+i, with L₁ ∈ {1,2,4,8}, m=^((L))−1, i=0, . . . , L₁−1,an additional cell c₂ can have a potential PDCCH candidate in positionL₂·{(Y_(k) ^(c) ² +2n+mod(m, 2)))mod └N_(CCE,k)/L₂┘}+j, L₂ ∈ {L₁, 2L₁}if L₁<8, L₂=L₁ if L₁=8, n=0, . . . , M^((L) ² ⁾/2−1, j=0, . . . , L₂−1.This process can directly extend to additional cells.

Additional restrictions for the third design are possible, for example,by requiring the same CCE aggregation level to be used in all cells. Thepotential combinations are covered by combinations of the principles forthe first and second designs as described by the third design.

The previously described PDCCH extension was compatible with existingsingle-cell communications. However, PDCCH extension may also besupported in a non-compatible manner. For this case, in accordance withan embodiment of the present invention, a different interpretation ofthe PCFICH values and a different configuration of the UE-CSS and UE-DSSmay apply. Unlike legacy systems for which the PCFICH conveys 3predetermined values for the PDCCH size, such as for example 1, 2, or 3OFDM symbols, the PCFICH for non-compatible PDCCH extension can conveymore values, which are not predetermined but can semi-statically vary.The Node B may broadcast a configuration of PDCCH sizes, from a set ofpossible configurations, and the PCFICH may then simply indicate onesize from the broadcasted configuration of PDCCH sizes. For example, theNode B may indicate one of the {1, 2, 3, 4}, {2, 3, 4, 5}, {3, 4, 5, 6}and {4, 5, 6, 7}, in number of OFDM symbols, for the PDCCH sizeconfiguration. The 2 bits in the PCFICH can then be used to inform theUEs of the PDCCH size within the configuration broadcasted by the NodeB.

FIG. 16 illustrates a PDCCH size extension by configuring a set ofpossible values and using a PCFICH to indicate one value in the set,according to an embodiment of the present invention.

Referring to FIG. 16, the Node B broadcasts 2 bits, for example, “10”,to indicate the PDCCH size configuration of {3, 4, 5, 6} symbols 1610.The PDCCH size configuration may take effect at a predeterminedsub-frame after the Node B broadcasts it, such as, for example, in thefirst sub-frame S, such that modulo(S, 40)=0. The PCFICH transmitted ineach sub-frame indicates an element from the PDCCH size configurationset, such as, for example, the third element 1620. The UE determines thePDCCH size based on both the broadcasted PDCCH size configuration andthe PCFICH value 1630.

In addition to configuring a total PDCCH size, an individual size of theUE-CSS or UE-DSS can also be configured. For example, the Node B maybroadcast the UE-CSS size. Consequently, A-UEs can know that the UE-CSSsize may have one of four predetermined values and the Node B simplybroadcasts 2 bits to indicate that value or to indicate that the UE-CSSsize is 1, 2, 3, or 4 times the basic UE-CSS size of 16 CCEs. Theindication of the UE-CSS size may also be implicit based on the PDCCHconfiguration size. For example, if the Node B broadcasts the thirdPDCCH configuration size in FIG. 16, A-UEs can identify that the UE-CSSis 3 times the basic UE-CSS size of 16-CCEs, i.e., the UE-CSS size is 48CCEs or it is determined by the third element in a configured set ofUE-CSS sizes such as, for example, a set of {16, 28, 36, 44} CCEs.

FIG. 17 illustrates explicit and implicit indication by the Node B of aUE-CSS size to A-UEs, according to an embodiment of the presentinvention.

Referring to FIG. 17, for explicit indication, the Node B informs A-UEsof the UE-CSS size through a broadcast channel, e.g., an SIBtransmission. For example, the Node B transmits 2 bits with a value “10”to indicate 36 CCEs, which is the third element in a set of 4 possibleUE-CSS sizes 1710. A-UEs, upon reception of that broadcast information,determine the UE-CSS for each cell 1720, as described above, for PDCCHextension compatible with legacy systems. For implicit indication, theNode B broadcasts the PDCCH size configuration (for example, in an SIB),as described in FIG. 17, and based on this configuration, A-UEsdetermine the UE-CSS size and the UE-CSS for each cell. For example, theNode B may broadcast the third PDCCH size configuration 1730 and thethen A-UEs determine the UE-CSS size to be 36 CCEs 1740.

While the present invention has been shown and described with referenceto certain embodiments thereof, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present invention asdefined by the appended claims, and any equivalents thereof.

What is claimed is:
 1. A method for monitoring downlink controlinformation in a communication system for supporting a plurality ofcells, the method comprising: acquiring a cell index for a cell, whereinthe cell index is defined based on a dedicated radio resource control(RRC) signaling; acquiring information for an orthogonal frequencydivision multiplex (OFDM) symbol and a resource block through thededicated RRC signaling; and monitoring a physical downlink controlchannel (PDCCH) on a dedicated search space associated with theinformation, wherein the dedicated search space is defined per each ofthe plurality of cells; and receiving a physical downlink shared channel(PDSCH) on the cell based on the monitored PDCCH, wherein the cell isone among the plurality of cells, wherein the dedicated search space isdefined based on an aggregation level, a number of PDCCH candidate forthe aggregation level, and an identifier configured for a user equipment(UE).
 2. The method of claim 1, wherein a cell of a PDCCH transmissionis defined by the dedicated RRC signaling.
 3. The method of claim 1,wherein inclusion of a carrier indicator is different between downlinkcontrol information formats.
 4. The method of claim 1, wherein inclusionof a carrier indicator is defined by the dedicated RRC signaling.
 5. Themethod of claim 1, wherein a value of a carrier indicator for the cellis implicitly defined.
 6. A method for transmitting downlink controlinformation in a communication system for supporting a plurality ofcells, the method comprising: transmitting information on a cell indexfor a cell, wherein the cell index is defined based on a dedicated radioresource control (RRC) signaling; transmitting information for anorthogonal frequency division multiplex (OFDM) symbol and a resourceblock through the dedicated RRC signaling; and transmitting a physicaldownlink control channel (PDCCH) on a dedicated search space associatedwith the information, wherein the dedicated search space is defined pereach of the plurality of cells; and transmitting a physical downlinkshared channel (PDSCH) on the cell based on the transmitted PDCCH,wherein the cell is one among the plurality of cells, wherein thededicated search space is defined based on an aggregation level, anumber of PDCCH candidate for the aggregation level, and an identifierconfigured for a user equipment (UE).
 7. The method of claim 6, whereina cell of a PDCCH transmission is defined by the dedicated RRCsignaling.
 8. The method of claim 6, wherein inclusion of a carrierindicator is different between downlink control information formats. 9.The method of claim 6, wherein inclusion of a carrier indicator isdefined by the dedicated RRC signaling.
 10. The method of claim 6,wherein a value of a carrier indicator for the cell is implicitlydefined.
 11. An apparatus for monitoring downlink control information ina communication system for supporting a plurality of cells, theapparatus comprising: a transceiver configured to transmit and receive asignal; and a processor coupled with the transceiver, wherein theprocessor is configured to: acquire a cell index for a cell, wherein thecell index is defined based on a dedicated radio resource control (RRC)signaling; acquire information for an orthogonal frequency divisionmultiplex (OFDM) symbol and a resource block through the dedicated RRCsignaling; and monitor a physical downlink control channel (PDCCH) on adedicated search space associated with the information, wherein thededicated search space is defined per each of the plurality of cells;and control the transceiver to receive a physical downlink sharedchannel (PDSCH) on the cell based on the monitored PDCCH, wherein thecell is one among the plurality of cells, wherein the dedicated searchspace is defined based on an aggregation level, a number of PDCCHcandidate for the aggregation level, and an identifier configured for auser equipment (UE).
 12. The apparatus of claim 11, wherein a cell of aPDCCH transmission is defined by the dedicated RRC signaling.
 13. Theapparatus of claim 11, wherein inclusion of a carrier indicator isdifferent between downlink control information formats.
 14. Theapparatus of claim 11, wherein inclusion of a carrier indicator isdefined by the dedicated RRC signaling.
 15. The apparatus of claim 11,wherein a value of a carrier indicator for the cell is implicitlydefined.
 16. An apparatus for transmitting downlink control informationin a communication system for supporting a plurality of cells, theapparatus comprising: a transceiver configured to: transmit informationon a cell index for a cell, wherein the cell index is defined based on adedicated radio resource control (RRC) signaling; transmit informationfor an orthogonal frequency division multiplex (OFDM) symbol and aresource block through the dedicated RRC signaling; and transmit aphysical downlink control channel (PDCCH) on a dedicated search spaceassociated with the information, wherein the dedicated search space isdefined per each of the plurality of cells; and transmit a physicaldownlink shared channel (PDSCH) on the cell based on the transmittedPDCCH, wherein the cell is one among the plurality of cells, wherein thededicated search space is defined based on an aggregation level, anumber of PDCCH candidate for the aggregation level, and an identifierconfigured for a user equipment (UE).
 17. The apparatus of claim 16,wherein a cell of a PDCCH transmission is defined by the dedicated RRCsignaling.
 18. The apparatus of claim 16, wherein inclusion of a carrierindicator is different between downlink control information formats. 19.The apparatus of claim 16, wherein inclusion of a carrier indicator isdefined by the dedicated RRC signaling.
 20. The apparatus of claim 16,wherein a value of a carrier indicator for the cell is implicitlydefined.